U.S. patent application number 09/882044 was filed with the patent office on 2002-01-03 for telecommunication carrier processor subsystem with in-band control and addressing via cell header fields.
This patent application is currently assigned to ALCATEL. Invention is credited to Lizin, Gilbert Carlo Marie.
Application Number | 20020001311 09/882044 |
Document ID | / |
Family ID | 8173743 |
Filed Date | 2002-01-03 |
United States Patent
Application |
20020001311 |
Kind Code |
A1 |
Lizin, Gilbert Carlo Marie |
January 3, 2002 |
Telecommunication carrier processor subsystem with in-band control
and addressing via cell header fields
Abstract
A telecommunication carrier processor subsystem (CPS) adapted to
receive cells (1, 2), preferably ATM cells, and to derive from the
H-bit header field thereof a smaller set of R bits. The set of R
bits is not only used to route the cell to a predetermined output
of the subsystem but is also combined with a second set of D bits
for replacing the VPI/VCI bits in the H-bit header field of the
cell. The second set of D bits may be used for transmitting
information data such as user data, control or command
transmission. It may also be used for hand-over process or cell
duplication and is then particularly suited for broadband local
access applications relating to low earth orbit satellite
constellations. Preserving the global ATM cell header size while
using the freed D bits after changing the connection identifier
range is called in-band control. It allows using off the shelf
components for the cell transmission between sub-systems, boards or
components. It also leads to the reduction of Connection Data
Tables in coherence with the dimensioning required for a processing
unit.
Inventors: |
Lizin, Gilbert Carlo Marie;
(Sambreville, BE) |
Correspondence
Address: |
SUGHRUE, MION, ZINN,
MACPEAK & SEAS, PLLC
2100 Pennsylvania Avenue, N.W.
Washington
DC
20037-3213
US
|
Assignee: |
ALCATEL
|
Family ID: |
8173743 |
Appl. No.: |
09/882044 |
Filed: |
June 18, 2001 |
Current U.S.
Class: |
370/392 ;
370/328; 370/397 |
Current CPC
Class: |
H04Q 11/0478 20130101;
H04L 49/3009 20130101; H04L 2012/5652 20130101; H04L 49/309
20130101; H04L 49/3081 20130101 |
Class at
Publication: |
370/392 ;
370/397; 370/328 |
International
Class: |
H04L 012/28 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 28, 2000 |
EP |
00401853.7 |
Claims
1. Telecommunication carrier processor subsystem (CPS) having an
input (IN) and a plurality of outputs (OUTi, OUTj, OUTk) and being
adapted to receive, at said input, telecommunication cells (1, 2)
each comprising a payload field and a H-bit header field, said
subsystem including telecommunication interface means (TID) having
an interface input corresponding to said input (IN) and a plurality
of outlets (OTLi, OTLj, OTLk) each coupled to distinct ones of said
outputs, said telecommunication interface means including header
detection means (HDC) connected to said input and routing means
(RTC) connected to said input, to said plurality of outlets and
controlled by said header detection means, said header detection
means being adapted to derive a R-bit connection identifier from at
least a portion of the set of H bits contained in said header
field, R and H being integer numbers with R smaller than H,
characterized in that said routing means (RTC) are adapted to
transmit a cell (1, 2) from said input (IN) to at least one
predetermined outlet of said plurality of outlets (OTLi, OTLj,
OTLk) according to said R-bit connection identifier received from
said header detection means (HDC), and to replace, into the header
field of said cell, said set of H bits by a second set of H bits
including the set of R bits constituting said connection
identifier.
2. Telecommunication carrier processor subsystem according to claim
1, characterized in that said telecommunication interface means
(TID) further includes header combination means (HCC) coupled to
said header detection means (HDC) and to said routing means (RTC)
and adapted to combine a set of D bits of information data with
said set of R bits received from said header detection means (HDC)
into said second set of H bits for replacing the first mentioned
set of H bits contained in said header field, D being an integer
number smaller or equal to the difference between H and R.
3. Telecommunication carrier processor subsystem according to claim
1, characterized in that said header detection means (HDC) includes
a routing table having as input said portion of the set of H bits
contained in said header field and as output said set of R bits
constituting said connection identifier.
4. Telecommunication carrier processor subsystem according to claim
1, characterized in that said telecommunication cells are
Asynchronous Transfer Mode [ATM] cells.
5. Telecommunication carrier processor subsystem according to claim
2, characterized in that said carrier processor subsystem (CPS)
further includes a plurality of carrier processor means (CPi) each
having an inlet connected to an outlet (OTLi) of said
telecommunication interface means (TID) and an output corresponding
to an output (OUTi) of said carrier processor subsystem, each
carrier processor means being adapted to transmitted or not to said
output a cell received at said inlet according to at least a
portion of the information data included in said set of D bits.
6. Telecommunication carrier processor subsystem according to claim
5, characterized in that each carrier processor means (CPi) of said
plurality includes parameter detection means (PDC) connected to
said inlet (OTLi) and carrier mapping means (CMC) connected to said
inlet, to said output (OUTi) and to an output (OPD) of said
parameter detection means, said parameter detection means being
adapted to extract said second set of H bits contained in the
header field of a cell received at said inlet, to translate said
second set of H bits into a set of M bits and to transmit said set
of M bits to said carrier mapping means.
7. Telecommunication carrier processor subsystem according to claim
6, characterized in that each of said carrier mapping means (CMC)
is adapted to replace in the header field of said cell said second
set of H bits by said set of M bits, prior to transmit said cell to
said output (OUTi).
Description
[0001] The present invention relates to a telecommunication carrier
processor subsystem having an input and a plurality of outputs and
being adapted to receive, at said input, telecommunication cells
each comprising a payload field and a H-bit header field, said
subsystem including telecommunication interface means having an
interface input corresponding to said input and a plurality of
outlets each coupled to distinct ones of said outputs, said
telecommunication interface means including header detection means
connected to said input and routing means connected to said input,
to said plurality of outlets and controlled by said header
detection means, said header detection means being adapted to
derive a R-bit connection identifier from at least a portion of the
set of H bits contained in said header field, R and H being integer
numbers with R smaller than H.
[0002] In the frame of low earth orbit satellite constellations
providing broadband local access solutions, the use of
telecommunication cells is well suited for the transport of
multimedia services. The cells permit to establish end-to-end
connections between, e.g., a transmitting external
telecommunication exchange or network coupled to the input and
terminals. These connections are possible via earth stations
comprising the telecommunication carrier processor subsystem,
modems and terrestrial antenna stations. The cells are so
transferred via satellites coupling the outlets of the
telecommunication interface means to the terminals.
[0003] To transmit a cell from the input to a predetermined outlet,
the routing means uses routing information that is generally
extracted from the H bits contained in the header filed of the
cell. However, the number of possible outlets and the number of
connections that the terminals coupled to these outlets can handle
represents only a part of the permitted number of connections that
may be indicated by H bits. This limited part may for instance be
represented by a set of R bits, where R is smaller than H. Due to
other considerations, it is an unsuitable constraint to split the
range indicated by the H bits into equal and contiguous fractions
only to solve implementation problems. As a consequence, an
interfacing device or header detection means is needed to derive
the R bits of "useful" routing information from the H bits of
"full" routing information contained in the header field of the
cell.
[0004] Such a header detection means is already known in the art,
e.g. from the European Patent Application EP-A1-0 862 348 entitled
"Interfacing device to extract M sets of bits out of N sets of
bits, control unit and logical cell". As indicated in that
document, the known header detection means or interfacing device is
particularly useful when several data-handling units are connected
to the outlets of a telecommunication interface means and different
ones of these data-handling units can be addressed by only a
portion of the data entering simultaneously at the input of the
device. This is for instance so when the incoming sets of data bits
are ATM [Asynchronous Transfer Mode] cells containing, in their
header field, information of which only a portion is needed to
further handle the cell. The known interfacing device may thus be
used to reduce the number of H bits contained in the header field
of a cell into a set of R bits sufficient to control the routing of
the cell through the telecommunication interface means. According
to the known document, such a set of R bits is then applied as a
pointer to a RAM [Random Access Memory] of which the output is a
connection identifier that controls the telecommunication interface
means.
[0005] The output cell provided at an outlet of the
telecommunication interface means is then either the former full
cell (payload and header) received at the input but associated to
the connection identifier issued from the RAM memory, or only the
payload field of the former cell associated to this connection
identifier. In any case, the length, i.e. the number of bits, of a
cell at an outlet of the telecommunication interface means differs
from the length of the former cell received at the input
thereof.
[0006] Because the cells at the input generally have a standardized
format, e.g. ATM cells, the design of specific apparatus able to
manipulate non-standardized cell formats is required at the outlets
of the telecommunication interface means. As a result, the
development of a telecommunication carrier processor subsystem is
relatively expensive and complex.
[0007] An object of the present invention is to provide a
telecommunication carrier processor subsystem of the above known
type but wherein the development cost and complexity of the
subsystem and associated devices are reduced.
[0008] According to the invention, this object is achieved due to
the fact that said routing means are adapted to transmit a cell
from said input to at least one predetermined outlet of said
plurality of outlets according to said R-bit connection identifier
received from said header detection means, and to replace, into the
header field of said cell, said set of H bits by a second set of H
bits including the set of R bits constituting said connection
identifier.
[0009] In this way, the global cell size or length of a cell at an
outlet of the routing means and thus also at the outlet of the
telecommunication interface means is identical to the length of a
cell received at the input thereof. As a consequence, if normalized
cells are applied at the input, normalized cells are also provided
at the outlets and standard components, devices and equipments may
be used to handle the cells inside and outside the
telecommunication carrier processor subsystem. This reduces the
cost and the complexity while increasing the performances and
generally saving power consumption.
[0010] Moreover, the R bits derived from a portion of the former
H-bit header and constituting the connection identifier are used
both to control the routing means and to give, to further devices,
indications about the cell. The former set of H bits contained in
the input cell is indeed in most applications no longer necessary
for the further processing of the cell.
[0011] Another characterizing embodiment of the present invention
is that said telecommunication interface means further includes
header combination means coupled to said header detection means and
to said routing means and adapted to combine a set of D bits of
information data with said set of R bits received from said header
detection means into said second set of H bits for replacing the
first mentioned set of H bits contained in said header field, D
being an integer number smaller or equal to the difference between
H and R.
[0012] The bits freed in the header field of a cell by replacing
the former portion of the set of H bits by a smaller set of R bits,
may be used for other purposes than routing without affecting the
above mentioned advantages of the invention. The portion_of_H minus
R=D freed bits are here preferably re-used for transmitting
information data such as user data, control or command
transmission, and this without changing the global cell size. This
last capability is called "in-band control".
[0013] In a preferred embodiment of the present invention, said
telecommunication cells are Asynchronous Transfer Mode [ATM]
cells.
[0014] The format of the cells is thus fully standardized whereby
standard equipment practice is applicable.
[0015] Also another characterizing embodiment of the present
invention is that said carrier processor subsystem further includes
a plurality of carrier processor means each having an inlet
connected to an outlet of said telecommunication interface means
and an output corresponding to an output of said carrier processor
subsystem, each carrier processor means being adapted to
transmitted or not to said output a cell received at said inlet
according to at least a portion of the information data included in
said set of D bits.
[0016] The carrier processor means is an interface between the
telecommunication interface means and the above-mentioned
satellites. To handle the traffic there between, one of the tasks
of a carrier processor means or earth station is to map the
telecommunication cells onto a functional MAC [Medium Access
Control] sub-layer. Another task of the carrier processor means,
together with the telecommunication interface means, is to handle
the hand-over from one satellite to another. Indeed, in these low
earth orbit satellite constellation contexts, a telecommunication
connection path may change during the connection life. When a
satellite disappears, the traffic must be handed-over to a new
upcoming satellite. The cells transmitted by a carrier processor
means dealing with the first satellite have then to be re-routed to
another carrier processor means communicating with the rising
satellite. For that operation there is a need to switch in real
time the path followed by the cells between carrier processors
means. Furthermore, together with the telecommunication interface
means, the carrier processor means may also be used to duplicate
cells toward several outputs. In any case, owing to the use of some
or all the bits of the set of D bits received with the cell, the
path switch or the connection duplication is done properly, i.e.
without any cell lost and without any cell sequence
perturbation.
[0017] In more detail, yet another characterizing embodiment of the
present invention is that each carrier processor means of said
plurality includes parameter detection means connected to said
inlet and carrier mapping means connected to said inlet, to said
output and to an output of said parameter detection means, said
parameter detection means being adapted to extract said second set
of H bits contained in the header field of a cell received at said
inlet, to translate said second set of H bits into a set of M bits
and to transmit said set of M bits to said carrier mapping
means.
[0018] Further characterizing embodiments of the present are
mentioned in the appended claims.
[0019] It is to be noticed that the term `comprising`, used in the
claims, should not be interpreted as being restrictive to the means
listed thereafter. Thus, the scope of the expression `a device
comprising means A and B` should not be limited to devices
consisting only of components A and B. It means that with respect
to the present invention, the only relevant components of the
device are A and B.
[0020] Similarly, it is to be noticed that the term `coupled`, also
used in the claims, should not be interpreted as being restrictive
to direct connections only. Thus, the scope of the expression `a
device A coupled to a device B` should not be limited to devices or
systems wherein an output of device A is directly connected to an
input of device B. It means that there exists a path between an
output of A and an input of B which may be a path including other
devices or means.
[0021] The above and other objects and features of the invention
will become more apparent and the invention itself will be best
understood by referring to the following description of an
embodiment taken in conjunction with the accompanying drawings
wherein:
[0022] FIG. 1 represents a carrier processor subsystem CPS
according to the invention and adapted to transmit
telecommunication cells to a terminal TE via a low earth orbit
satellite constellation;
[0023] FIGS. 2a to 2c show contents of the header field of a cell
used in the carrier processor subsystem CPS of FIG. 1;
[0024] FIG. 3 represents in more detail a telecommunication
interface device TID forming part of the carrier processor
subsystem CPS of FIG. 1; and
[0025] FIG. 4 represents in more detail one of the carrier
processor devices CPi forming part of the carrier processor
subsystem CPS of FIG. 1.
[0026] The telecommunication carrier processor subsystem CPS shown
at FIG. 1 forms part of a gateway of a broadband telecommunication
local access network. The telecommunication access network receives
cells from an external telecommunication network or exchange (not
shown) and transmits them to terminals via the carrier processor
subsystem CPS and a low earth orbit satellite constellation. The
carrier processor subsystem CPS has an input IN coupled to the
external network for receiving cells, as 1 and 2, thereof and has
several outputs, of which only three OUTi, OUTj and OUTk are shown.
The outputs OUTi, OUTj and OUTk are connected to terrestrial
antenna stations TAi, TAj and TAk via respective modems MDi, MDj
and MDk. The terrestrial antenna stations TAi, TAj and TAk are
adapted to communicate with terminals, such as TE, via satellites
of the constellation. Although only two satellites SAT1 and SAT2
are shown at FIG. 1, a low earth orbit satellite constellation
contains for instance 66 satellites each moving according to a
predetermined trajectory. The operation of the terrestrial antenna
stations TAi, TAj and TAk, of the modems MDi, MDj and MDk, of the
satellites SAT1 and SAT2, and of the terminal TE will not be
described in more detail hereafter because it is supposed to be
known by any person normally skilled in the art.
[0027] The carrier processor subsystem CPS includes a
telecommunication interface device TID and several carrier
processor units, of which only three CPi, CPj and CPk are shown.
The telecommunication interface device TID has an input IN
connected to the like-named input of the subsystem and several
outlets OTLi, OTLj and OTLk each connected a like-named inlet of a
corresponding carrier processor unit CPi, CPj and CPk. Each carrier
processor unit further has an output connected to a corresponding
output of the subsystem CPS.
[0028] The telecommunication cells 1, 2 applied to the input IN of
the carrier processor subsystem CPS preferably have a standardized
format and are for instance of the ATM [Asynchronous Transfer Mode]
type. The ATM technology is well suited for the transport of
multimedia services in the present case of low earth orbit
satellite constellations providing broadband local access
solutions. In this context of satellites, an ATM connection path is
not unchanging during the connection life. When a satellite, say
SAT1, disappears, i.e. with it becomes unreachable for the carrier
processor subsystem CPS and more particularly for the terrestrial
antenna stations TAi thereof or for the considered terminal TE, the
traffic to the terminal TE must be handed-over to a new upcoming
satellite, say SAT2. All the ATM cells of this traffic have then to
be re-routed in real time from the carrier processor unit CPi
dealing with the satellite SAT1 to the carrier processor unit CPk
communicating with the rising satellite SAT2. The operation to
switch in real time the path followed by the ATM cells 1, 2 between
carrier processor units CPi and CPk is performed by the
telecommunication interface device TID.
[0029] An ATM cell has a length or global size of 53 bytes and
comprises a header field and a payload field as shown at FIG. 2a.
As shown at FIG. 2b, the header has a predetermined length, say of
H bits, and comprises, amongst other, a Virtual Path Identifier VPI
and a Virtual Channel Identifier VCI that identify an ATM
connection, e.g. the destination address of the terminal TE to
which the cell is intended. Depending the type of ATM interface
used, the complete range of the VPI/VCI identifiers permits either
2.sup.8+16=16 777 216 (in case of User-Network Interface) or
2.sup.12+16=268 435 456 (in case Network-Node Interface) values.
However, due to the available implementation technology and/or the
product requirements, a carrier processor unit, as CPi, can only
handle a part of this number of possible connections. The limited
number of connections, say for instance 2.sup.R, may be taken
anywhere in the ATM connection identifier range given by VPI/VCI
and will be called Internal Connection Identifier ICID as shown at
FIG. 2c. The value R will be chosen smaller than 24 or 28 depending
on the interface type. For R=16, the gain in size is of
2.sup.12+16-2.sup.R=268 369 920 values removed. Further in this
description, we will generally consider that only the portion of
the header comprising the VPI/VCI fields is taken into account and
that the Internal Connection Identifier ICID has a length of R
bits, where R is an integer value smaller than the considered
portion of H bits of the header. The remaining part of this portion
of the H bits, say RB that is a set of D free bits with
D=portion_of_H-R, may be used for other purposes such as hand-over
process or cell duplication as will be explained later.
[0030] The telecommunication interface device TID will be described
in more detail hereafter by making reference to FIG. 3. TID
includes a routing circuit RTC having an input IN connected to the
like-named input of the subsystem CPS and is adapted to route the
incoming cell to one (or more) of the outlets OTLi, OTLj or OTLk of
TID. This routing is performed under control of a header detection
circuit HDC also included in the interface device TID. The header
detection circuit HDC also has an input IN connected to the
like-named input of TID and an output CTL connected to a like-named
control input of the routing circuit RTC. HDC is adapted to read
the set of H bits contained in the header field of an incoming cell
and to derive from there the set of R bits corresponding to the
above internal connection identifier ICID. Due to ATM
considerations, it is generally not sufficient to simply split the
VPI/VCI range of the set of H bits into equal and/or contiguous
fractions only to solve implementation problems. Very often,
connection data tables with the necessary ATM connection range are
required inside the header detection circuit HDC. However, owing to
the reduction from the portion VPI/VCI of the H bits to R bits,
board space is saved anyway in the HDC, as a consequence of which
the power consumption is also reduced. The operation of deriving
the set of R bits from the set of H bits is not described in more
detail hereafter since such an operation is for instance already
explained in the above-mentioned European Patent Application
EP-A1-0 862 348. It is for instance performed by means of a routing
table included in the header detection means HDC and having as
input the portion VPI/VCI of the H bits header and as output the
set of R bits constituting the internal connection identifier
ICID.
[0031] The R bits identifier ICID received by the routing circuit
RTC via its control input CTL is used to select a particular one of
its outlets. RTC further also replaces, in the header field of the
cell, the former set of H bits with a new set of H bits wherein the
portion VPI/VCI now comprises the set of R bits provided by the
header detection means HDC and the above set of D bits. The global
size or length of the cell at the outlet of the routing circuit RTC
is thus not modified and this last capability is named in-band
control. As a result thereof, standard components and devices may
be used to handle the cells all through the carrier processor
subsystem CPS.
[0032] The telecommunication interface device TID also comprises a
header combination circuit HCC having an input connected to the
output CTL of the header detection circuit HDC and an output
coupled to an input of the routing circuit RTC. The header
combination circuit HCC has another input DIN, external to the
interface device TID, and to which external information data may be
applied. This information data is intended to be loaded into the
set of D bits in the header field of the cell. The merging of the
set of R bits and the set of D bits into a new portion, and thus a
new set, of H bits of the header field occurs in the routing
circuit RTC.
[0033] From the outlets OTLi, OTLj and OTLk of the routing circuit
RTC, and thus also of the interface device TID, the cells are
transmitted to like-named inlets of the carrier processor units
CPi, CPj and CPk respectively. One of these carrier processor
units, say CPi, is represented at FIG. 4. CPi includes a carrier
mapping circuit CMC having an inlet OTLi connected to the
like-named inlet of CPi and an output OUTi connected to the
like-named output of CPi, OUTi being also an output of the
telecommunication carrier processor subsystem CPS. The carrier
processor unit CPi further comprises a parameter detection circuit
PDC having an inlet OTLi connected to the like-named inlet of CPi
and an output OPD connect to a like-named control input of the
carrier mapping circuit CMC. The parameter detection circuit PDC is
adapted to extract the set of H bits contained in the header field
of the cell received at the inlet OTLi, to translate this set into
another set of M bits and to transmit the new set of M bits to the
carrier mapping circuit CMC via the output OPD.
[0034] To handle the telecommunication traffic, one of the tasks of
an earth station or more particularly of a carrier mapping circuit
CMC is to map the ATM cells onto a functional MAC [Medium Access
Control] sub-layer. To this end, the carrier mapping circuit CMC of
the carrier processor unit CPi replaces, in the header field of the
received cell, the set of H bits by a set of M bits compatible with
the Medium Access Control protocol used by the carrier processor
subsystem CPS. The modified cell is then transmitted to the output
OUTi of CPS.
[0035] The above part RB of the header field containing D liberated
bits may be used for switching between carrier processor units or
for duplication purpose.
[0036] In case of switching, e.g. to change of satellite
connection, one or more of the freed D bits are used as in-band
control. For example, one of the D bits is used as a Switch Bit
Flag SWF (not shown). Suppose an existing connection whereby the
cells, say cell 1 as referring to FIG. 1, follow an initial path
from the output OTLi of the telecommunication interface device TID
to the like-named inlet of the carrier processor unit CPi. As long
as SWF=0, nothing is changing this state. When a hand-over time
occurs, e.g. just before the satellite SAT1 disappears and when
SAT2 becomes reachable, the connection must proceed through the
carrier processor unit CPk rather than through CPi. The switch bit
flag SWF is then activated, i.e. SWF=1. The carrier processor unit
CPi is thereby informed that it must now discard the incoming cells
of this connection, whilst the carrier processor unit CPk is
informed that it must now take in charge such cells. The cells of
the connection, say cell 2, now follow the new path via the output
OTLk.
[0037] As already mentioned, the present carrier processor
subsystem CPS and more particularly its telecommunication interface
device TID is also adapted to duplicate the ATM cells toward
several carrier processor units without any cell lost and without
any cell sequence perturbation.
[0038] In this case of duplication, a Duplication Bit Flag DPF (not
shown) belonging to the set of D bits is used. By receiving the DPF
bit, the carrier processor unit CPi do not change anything in its
behavior, while the carrier processor unit k reacts exactly as for
the switch bit flag SWF. The operation may be repeated n times in
order to establish n+1 paths for a particular connection. The
duplication application controlled by the set of D bits in the ATM
cell header may be also useful in case of a hand-over anticipation
procedure or in case of broadcast connections.
[0039] It is to be noted that, for instance for another
application, the carrier processor unit CPi is also adapted to
translate the internal connection identifier ICID again to the
correct VPI/VCI value identical or not to the original one. This
solution is also applicable only on the VPI field, e.g. when an
access node has to be transparent for the VCI.
[0040] A final remark is that embodiments of the present invention
are described above in terms of functional blocks. From the
functional description of these blocks, given above, it will be
apparent for a person skilled in the art of designing electronic
devices how embodiments of these blocks can be manufactured with
well-known electronic components. A detailed architecture of the
contents of the functional blocks hence is not given.
[0041] While the principles of the invention have been described
above in connection with specific apparatus, it is to be clearly
understood that this description is made only by way of example and
not as a limitation on the scope of the invention, as defined in
the appended claims.
* * * * *